Yes, you can define a class inside an interface. In general, if the methods of the interface use this class and if we are not using it anywhere else we will declare a class within an interface.Exampleinterface Library {    void issueBook(Book b);    void retrieveBook(Book b);    public class Book {       int bookId;       String bookName;       int issueDate;       int returnDate;    } } public class Sample implements Library {    public void issueBook(Book b) {       System.out.println("Book Issued");    }    public void retrieveBook(Book b) { ... Read More

An interface with no methods in it is referred to as a marker interface, also known as a tagging interface. There are two basic design purposes of marker interfaces. Creates a common parent  It is used to provide a common parent interface for a group of related interfaces. When an interface like "eventlistener" is extended by dozens of other interfaces in the Java API, we can use a marker interface to create a common parent among a group of interfaces. For example, when an interface extends EventListener, the JVM knows that this particular interface is going to be used in an ... Read More

The flush() method of the FileWriter class flushes the contents of the file. You can use this method to truncate a file.Exampleimport java.io.File; import java.io.FileWriter; public class FileTruncate {    public static void main(String args[]) throws Exception {       File file = new File("myData");       FileWriter fw = new FileWriter(file, false);       fw.flush();       System.out.println("File truncated");    } }OutputFile truncated

You can access a plain text using the File class.ExampleLive Demoimport java.io.File; public class ReadFile {    public static void main(String[] args) {       File f = null;       String str = "data.txt";       try {          f = new File(str);          boolean bool = f.canExecute();          String a = f.getAbsolutePath();          System.out.print(a);          System.out.println(" is executable: "+ bool);       } catch (Exception e) {          e.printStackTrace();       }    } }Output C:\Users\data is executable: true

You can create a PDF file using the PDF Box library. You can set the environment for pdf box by following Pdf Box Environment Tutorial. Example import java.io.IOException; import org.apache.pdfbox.pdmodel.PDDocument; import org.apache.pdfbox.pdmodel.PDPage; public class CreatingEmptyPdf { public static void main(String args[]) throws IOException { PDDocument document = new PDDocument(); document.addPage(new PDPage()); document.save("C:/pdfBox/BlankPdf.pdf"); System.out.println("PDF created"); document.close(); } } Output PDF created

File class provides various methods to perform respective file operations.canRead(): This method tests whether the application can read the file denoted by this abstract pathname. It returns true if and only if the file specified by this abstract pathname exists and can be read by the application; false otherwise.canWrite(): This method tests whether the application can modify the file denoted by this abstract pathname. It returns true if and only if the file system actually contains a file denoted by this abstract pathname and the application is allowed to write to the file; false otherwise.createNewFile(): This method atomically creates a ... Read More

You can sort an array using sort() method of the Arrays class.ExampleLive Demoimport java.util.Arrays; public class MainClass {    public static void main(String args[]) throws Exception {       int array[] = { 2, 5, -2, 6, -3, 8, 0, -7, -9, 4 };       Arrays.sort(array);       printArray("Sorted array", array);       int index = Arrays.binarySearch(array, 1);       System.out.println("Didn't find 1 @ " + index);       int newIndex = -index - 1;       array = insertElement(array, 1, newIndex);       printArray("With 1 added", array);    }   ... Read More

You can get the size of a directory with the help of FileUtils.sizeofDirectory(File Name) method of FileUtils class.Exampleimport java.io.File; import org.apache.commons.io.FileUtils; public class Main {    public static void main(String[] args) {       long size = FileUtils.sizeOfDirectory(new File("C:/Windows"));       System.out.println("Size: " + size + " bytes");    } }OutputSize: 2048 bytes

Following example shows the way to look for a particular file in a directory by creating a File filter. Following example displays all the files having file names beginning with 'b'.ExampleLive Demoimport java.io.*; public class Main {    public static void main(String[] args) {       File dir = new File("C:");             FilenameFilter filter = new FilenameFilter() {          public boolean accept (File dir, String name) {             return name.startsWith("b");          }       };       String[] children = ... Read More

The java.io.File.mkdirs() creates the directory named by this abstract pathname, together with necessary and non-existent parent directories.ExampleLive Demoimport java.io.File; public class Main {    public static void main(String[] args) {       String directories = "D:\a\b\c\d ";       File file = new File(directories);       boolean result = file.mkdirs();       System.out.println("Status = " + result);    } }OutputStatus = true